Apparatus and method for transmitting and receiving a signal in a wireless communication system

ABSTRACT

A method and apparatus for transmitting and receiving a signal in a wireless communication system. The wireless communication system includes a transmitter with at least four transmit antennas and a receiver with at least one receive antenna. Space Frequency Block Coding (SFBC) processes are performed for input signals on a basis of two antenna pairs. Signal blocks whose number corresponds to the number of transmit antennas are output. A Space Time Block Coding (STBC) process is performed for the signal blocks generated according to the antenna pairs. Signals carried by single carriers are transmitted through the at least four transmit antennas mapped to the signal blocks.

PRIORITY

This application claims priority under 35 U.S.C. §119 to an applicationfiled in the Korean Intellectual Property Office on Dec. 30, 2005 andassigned Serial No. 2005-135410, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a signal transmission andreception in a communication system, and more particularly to anapparatus and method for transmitting and receiving a signal in a SpaceTime Frequency Block Code (STFBC) scheme in a communication system basedon a single carrier transmission.

2. Description of the Related Art

Recently, the transmit diversity technology has been proposed which canincrease channel capacity and link reliability by spatially arrangingmultiple transmit antennas without increasing a bandwidth ortransmission power. A Single Carrier-Frequency Domain Equalization(SC-FDE) scheme has been proposed which exploits Space Time Block Coding(STBC) for providing transmit diversity gain.

FIG. 1 illustrates a structure of the conventional STBC transmissionsequence.

Referring to FIG. 1, STBC data is transmitted through two antennas 101and 103. At this time, symbol blocks 110, 120, 130, and 140 aresequentially transmitted in a time domain. Cyclic Prefixes (CPs) 112,122, 132, and 142, serving as guard intervals, are inserted between thesymbol blocks 110, 120, 130, and 140. At this time, two symbol blocks,i.e., n-th blocks 110 and 130, to be transmitted through the twoantennas 101 and 103, are to have the same channel state.

When the STBC scheme is applied to a single carrier transmission scheme,for example, an SC-FDE scheme, the same channel state is maintainedbetween the symbol blocks in a slow fading environment, such thatperformance is guaranteed. There is a problem, however, in that theperformance is not guaranteed in a fast fading environment.

Furthermore, a Space Frequency Block Coding (SFBC) scheme is more robustto the fading environment in comparison with the STBC scheme. However,because the SFBC scheme is a multi-carrier scheme for applying a blockcode to a neighbor subchannel or carrier, it cannot be directly appliedto the single carrier transmission scheme, i.e., the SC-FDE scheme. Eventhough the SFBC scheme is applied to the single carrier transmissionscheme, its performance is guaranteed in a frequency non-selectivefading channel, but degrades in a frequency selective fading channel.

Thus, when channel characteristics of a communication system are fastfading channel and frequency selective fading channel, and specifically,when the STBC or SFBC scheme is applied to the single carriertransmission system, the overall system performance can be degraded inthe channels with the above-described channel characteristics.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide anapparatus and method for transmitting and receiving a signal in awireless communication system based on a Space Time Frequency Block Code(STFBC) scheme using a Single Carrier-Frequency Domain Equalization(SC-FDE) scheme based on a single carrier transmission.

It is another object of the present invention to provide an apparatusand method for transmitting and receiving a signal in a wirelesscommunication system based on a Space Time Frequency Block Code (STFBC)scheme that can avoid performance degradation in a fast fading channeland a frequency selective fading channel.

In accordance with an aspect of the present invention, there is provideda method for transmitting a signal in a wireless communication systemhaving a transmitter with at least four transmit antennas and a receiverwith at least one receive antenna, the method including performing SpaceFrequency Block Coding (SFBC) processes for input signals on a basis oftwo antenna pairs and outputting signal blocks whose number correspondsto the number of transmit antennas; and performing a Space Time BlockCoding (STBC) process for the signal blocks generated according to theantenna pairs, and transmitting signals carried by single carriersthrough the at least four transmit antennas mapped to the signal blocks.

In accordance with another aspect of the present invention, there isprovided a method for receiving a signal in a wireless communicationsystem having a transmitter with at least four transmit antennas and areceiver with at least one receive antenna, the method includingreceiving a signal through the at least one receive antenna; removingguard intervals from a first signal of the received signal and a secondsignal obtained by delaying the received signal by a regular time;performing serial to parallel conversion processes for the first andsecond signals from which the guard intervals have been removed andperforming Fast Fourier Transform (FFT) processes for parallel signals;combining the signals for which the FFT processes have been performed;solving simultaneous equations to remove components other than originalsignals from the combined signals; performing a Frequency DomainEqualization (FDE) process for signals obtained by solving thesimultaneous equations; demultiplexing the signals for which the FDEprocess has been performed and performing FFT processes for thedemultiplexed signals; and multiplexing the signals for which the FFTprocesses have been performed and performing signal recovery.

In accordance with another aspect of the present invention, there isprovided an apparatus for transmitting a signal in a wirelesscommunication system having a transmitter with at least four transmitantennas and a receiver with at least one receive antenna, the apparatusincluding a symbol mapper for mapping an input bit stream to a symbol ofa predetermined length; a Space Time Frequency Block Code (STFBC)encoder for performing Space Frequency Block Coding (SFBC) processes forinput signals on a basis of two antenna pairs, outputting signal blockswhose number corresponds to the number of transmit antennas, andperforming a Space Time Block Coding (STBC) process for the signalblocks generated according to the antenna pairs; and guard intervalinserters for inserting guard intervals into output signals of the STFBCencoder and transmitting the signals into which the guard intervals havebeen inserted through the at least four transmit antennas.

In accordance with yet another aspect of the present invention, there isprovided an apparatus for receiving a signal in a wireless communicationsystem having a transmitter with at least four transmit antennas and areceiver with at least one receive antenna, the apparatus including adelay unit for generating a second signal by delaying a signal receivedthrough the at least one receive antenna by a regular time; guardinterval removers for removing guard intervals from a first signalreceived through the at least one receive antenna and the second signal;serial to parallel converters for performing serial to parallelconversion processes for the signals from which the guard intervals havebeen removed; first Fast Fourier Transform (FFT) processors forperforming FFT processes for parallel signals; a linear combiner forcombining the signals for which the FFT processes have been performed; asimultaneous equation solver for solving simultaneous equations toremove components other than original signals from the combined signals;a Single Carrier-Frequency Domain Equalization (SC-FDE) processor forperforming an FDE process for signals obtained by solving thesimultaneous equations; demultiplexers for demultiplexing the signalsfor which the FDE process has been performed; second FFT processors forperforming FFT processes for the demultiplexed signals; and amultiplexer for multiplexing the signals for which the FFT processeshave been performed and performing signal recovery.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and aspects of the present invention will bemore clearly understood from the following detailed description taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a structure of a conventional Space Time Block Coding(STBC) transmission sequence;

FIG. 2 illustrates a structure of a transceiver based on SingleCarrier-Frequency Domain Equalization (SC-FDE) with a single transmitantenna;

FIG. 3 is a diagram illustrating a virtual structure of a transceiver ina communication system using Space Frequency Block Coding (SFBC);

FIG. 4 illustrates a structure of a transmitter in a communicationsystem using a Space Time Frequency Block Code (STFBC) scheme inaccordance with the present invention;

FIG. 5 illustrates a structure of an STFBC transmission sequence inaccordance with the present invention;

FIG. 6 illustrates a structure of a receiver in the communication systemusing the STFBC scheme in accordance with the present invention; and

FIG. 7 is a graph illustrating a performance curve of the communicationsystem using the STFBC scheme in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described in detail hereinbelow with reference to the accompanying drawings. In the followingdescription, detailed descriptions of functions and configurationsincorporated herein that are well known to those skilled in the art areomitted for clarity and conciseness.

The present invention generally relates to a signal transmission andreception in a communication system, and more particularly to a signaltransmission and reception in a Space Time Frequency Block Code (STFBC)scheme. The present invention provides the STFBC scheme using both aSpace Time Block Coding (STBC) scheme and a Space Frequency Block Coding(SFBC) scheme in a communication system based on a single carriertransmission. The STFBC scheme has advantages of both the STBC and SFBCschemes.

FIG. 2 illustrates a structure of a transceiver based on SingleCarrier-Frequency Domain Equalization (SC-FDE) with a single transmitantenna. The transmitter includes a bit generator 201, a symbol mapper203, a Cyclic Prefix (CP) inserter 205, a Digital to Analog Converter(DAC) 207, and a Radio Frequency (RF) transmitter 209.

Also, a receiver includes an RF receiver 211, an Analog to DigitalConverter (ADC) 213, a CP remover 215, a Fast Fourier Transform (FFT)processor 217, a Frequency Domain Equalization (FDE) processor 219, anInverse Fast Fourier Transform (IFFT) processor 221, a symbol demapper223, and a signal decider 225.

Referring to the operation of the transmitter, the bit generator 201generates information bits and outputs the generated information bits tothe symbol mapper 203. The symbol mapper 203 maps a bit stream outputfrom the bit generator 201 to a symbol of a regular length, and outputsthe symbol to the CP inserter 205.

The CP inserter 205 inserts a predetermined guard interval, i.e., a CP,into the symbol output from the symbol mapper 203, and outputs thesymbol into which the CP has been inserted to the DAC 207. The DAC 207converts a digital signal output from the CP inserter 205 to an analogsignal and outputs the analog signal to the RF transmitter 209. The RFtransmitter 209 transmits the analog signal carried by the radiofrequency through an antenna.

Referring to the operation of the receiver, the RF receiver 211 receivesa signal through an antenna and outputs the received signal to the ADC213. The ADC 213 converts the analog signal output from the RF receiver211 to a digital signal and outputs the digital signal to the CP remover215. The CP remover 215 removes a CP from the digital signal of the ADC213 and outputs the digital signal from which the CP has been removed tothe FFT processor 217.

The FFT processor 217 performs an FFT process on the output signal ofthe CP remover 215. The FDE processor 219 performs an FDE process on anoutput signal of the FFT processor 217. The IFFT processor 221 performsan IFFT process on an FDE signal of the FDE processor 219 and outputs anIFFT signal to the symbol demapper 223.

The symbol demapper 223 demaps a bit stream from a symbol of the outputsignal of the IFFT processor 221 and outputs the bit stream to thesignal decider 225. The signal decider 225 decides a transmitted signalfrom the bit stream of the symbol demapper 223.

The transceiver structure of the communication system based on theSC-FDE scheme has been described with reference to FIG. 2. A singlecarrier transmission sequence is designed and used to directly apply theSFBC of an existing Orthogonal Frequency Division Multiplexing (OFDM)scheme to the communication system using a single carrier. For this, theproposed SFBC scheme will be described with reference to FIG. 3, whichillustrates a structure of a transceiver in a communication system usingthe SFBC.

Referring to FIG. 3, for example, a transmitter with two antennasincludes a symbol mapper 310, a virtual signal processor 320, CPinserters 331 and 333, and antennas 341 and 343.

The symbol mapper 310 maps a bit stream input from the bit generator 201to a symbol of a regular length, and outputs the mapped bit stream tothe virtual signal processor 320. Herein, the virtual signal processor320 includes FFT processors 321 and 323 for performing N-point FFTprocesses and IFFT processors 325 and 327 for performing N-point IFFTprocesses.

The virtual signal processor 320 outputs two signal streams through onepair of the FFT processors 321 and 323 and the IFFT processors 325 and327 mapped thereto. The CP inserters 331 and 333 insert CPs into therespective signal streams and transmit the signal streams into which theCPs have been inserted through the antennas 341 and 343. The virtualsignal processor 320 conceptually shows a process for generating atime-domain single-carrier transmission signal to which the SFBC hasbeen applied. The virtual signal processor 320 is not actually presentin the structure of the transmitter of the present invention. When blockcodes for two transmit antennas and two neighbor frequency sub-channelsafter the FFT processors 321 and 323 are applied, time-domaintransmission samples for the respective antennas can be easily generatedand output through the IFFT processors 325 and 327. In relation to thesymbol output from the symbol mapper 310, the time-domain transmissionsamples of the IFFT processors 325 and 327 are simply generated usingsymmetric characteristics of a Fourier transform as shown in Equation(1).x ^(·)(−n)_(N)

X ^(·)(k), n,k=1, . . . , N−1  (1)

When the n-th symbol of a block to be transmitted from the i-th antennais denoted by x_(i)(n), the transmission symbol of the first antenna canbe expressed as shown in Equation (2).

$\begin{matrix}\begin{matrix}{{x_{1}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{1}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{1}\left( {2v} \right)} + {W_{N}^{- n}{X_{1}\left( {{2v} + 1} \right)}}} \right)W_{\frac{N}{2}}^{- {nv}}}}}} \\{{= {\frac{1}{\sqrt{2}}\left( {{x^{e}(n)} + {W_{N}^{- n}{x^{o}(n)}}} \right)}},{n = 0},1,\ldots\mspace{14mu},{N - 1}}\end{matrix} & (2)\end{matrix}$

Herein, x^(e)(n) and x^(o)(n) can be expressed as shown in Equation (3).

$\begin{matrix}{{{x^{e}(n)} = {\sqrt{\frac{2}{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{{X_{1}\left( {2v} \right)}W_{\frac{N}{2}}^{- {nv}}}}}},{{x^{o}(n)} = {\sqrt{\frac{2}{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{{X_{1}\left( {{2v} + 1} \right)}W_{\frac{N}{2}}^{- {nv}}}}}}} & (3)\end{matrix}$

Because x^(e)(n) and x^(o)(n) have a period of N/2 with respect to n,they can be replaced with

$x^{e}\left( (n)_{\frac{N}{2}} \right)$and

${x^{o}\left( (n)_{\frac{N}{2}} \right)}.$

Thus, scaling factors of the IFFT processors are adjusted in Equation(3) such that normal transmission power can be set to one. FromEquations (1) and (2), the transmission symbol of the second antenna canbe expressed as shown in Equation (4).

$\begin{matrix}\begin{matrix}{{x_{2}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{2}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{- {X_{1}^{*}\left( {{2v} + 1} \right)}} + {W_{N}^{- n}{X_{1}^{*}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nv}}}}}} \\{= {\frac{1}{\sqrt{2}}\left\lbrack {{- {x^{o^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}} + {W_{N}^{- n}{X^{e^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right\rbrack}}\end{matrix} & (4)\end{matrix}$

From the second and third lines of Equation (4), it can be seen that theSFBC has been applied.

FIG. 4 illustrates a structure of a transmitter in a communicationsystem using the STFBC scheme in accordance with the present invention.The transmitter includes a symbol mapper 401, an STFBC encoder 403, CPinserters 413, 415, 417, and 419, and antennas 421, 423, 425, and 427.

The symbol mapper 401 maps a bit stream input from the bit generator 201to a symbol of a regular length and outputs the symbol to the STFBCencoder 403. In this case, the STFBC encoder 403 includes SFBC encoders405 and 407 and an STBC encoder 409. An example in which SFBC and STBCprocesses are performed for the symbol and the transmitter structurehaving four transmit antennas will be described with reference to FIG.5. Signals of the STFBC encoder 403 to be transmitted through therespective antennas in the t-th time interval are defined in Equation(5).

$\begin{matrix}{\begin{matrix}{{x_{a\; 0}^{\prime}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{0}^{\prime}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{0}\left( {2v} \right)} - {W_{N}^{- n}{X_{2}^{*}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{2}}\left( {{x_{0}(n)} - {W_{N}^{- n}{x_{2}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right)}}\end{matrix}\begin{matrix}{{x_{a\; 1}^{\prime}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{1}^{\prime}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{1}\left( {2v} \right)} - {W_{N}^{- n}{X_{3}^{*}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{2}}\left( {{x_{1}(n)} - {W_{N}^{- n}{x_{3}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right)}}\end{matrix}\begin{matrix}{{x_{a\; 2}^{\prime}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{2}^{\prime}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{2}\left( {2v} \right)} - {W_{N}^{- n}{X_{0}^{*}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{2}}\left( {{x_{2}(n)} - {W_{N}^{- n}{x_{0}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right)}}\end{matrix}\begin{matrix}{{x_{a\; 3}^{\prime}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{3}^{\prime}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{3}\left( {2v} \right)} - {W_{N}^{- n}{X_{1}^{*}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{2}}\left( {{x_{3}(n)} - {W_{N}^{- n}{x_{0}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right)}}\end{matrix}} & (5)\end{matrix}$

x′_(lxi) (n) denotes the n-th symbol of a block to be transmitted fromthe i-th antenna in the t-th time interval. For blocks constructed bySTFBC symbols, the first CP inserter 413 inserts a CP to transmit ablock through the first antenna 421, the second CP inserter 415 insertsa CP to transmit a block through the second antenna 423, the third CPinserter 417 inserts a CP to transmit a block through the third antenna425, and the fourth CP inserter 419 inserts a CP to transmit a blockthrough the fourth antenna 427. Signals to be transmitted through therespective antennas in the next (t+T)-th time interval is defined inEquation (6).

$\begin{matrix}{\begin{matrix}{{x_{a\; 0}^{i + T}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{0}^{t + T}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{- {X_{1}^{*}\left( {2v} \right)}} + {W_{N}^{- n}{X_{3}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{2}}\left( {{- {x_{1}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}} + {W_{N}^{- n}{x_{3}(n)}}} \right)}}\end{matrix}\begin{matrix}{{x_{a\; 1}^{i + T}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{1}^{t + T}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{0}^{*}\left( {2v} \right)} - {W_{N}^{- n}{X_{2}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{2}}\left( {{x_{0}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)} + {W_{N}^{- n}{x_{2}(n)}}} \right)}}\end{matrix}\begin{matrix}{{x_{a\; 2}^{i + T}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{2}^{t + T}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{- {X_{3}^{*}\left( {2v} \right)}} + {W_{N}^{- n}{X_{1}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{2}}\left( {{- {x_{3}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}} + {W_{N}^{- n}{x_{1}(n)}}} \right)}}\end{matrix}\begin{matrix}{{x_{a\; 3}^{i + N}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{3}^{t + T}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{2}^{*}\left( {2v} \right)} + {W_{N}^{- n}{X_{0}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nk}}}}}} \\\left. {= {\frac{1}{\sqrt{2}}\left( {{x_{2}^{*}\left( \left( {- n} \right)_{\frac{N}{2}} \right)} + {W_{N}^{- n}{x_{1}(n)}}} \right)}} \right)\end{matrix}} & (6)\end{matrix}$

Equation (6) defines block symbols to be transmitted in the (t+T)-thtime interval. The blocks as shown in FIG. 5 are transmitted through theCP inserters 413, 415, 417, and 419 and the antennas 421, 423, 425, and427.

A sequence structure constructed by the blocks to be transmitted throughthe transmitter of FIG. 4 will be described with reference to FIG. 5.

FIG. 5 illustrates a structure of an STFBC transmission sequence inaccordance with the present invention, where the 2j-th and (2j+1)-thblocks are transmitted through the i-th antenna. Symbols x_(i) ^(2j)(n)of the 2j-th block are defined in Equation (7).

$\begin{matrix}{\begin{matrix}{{x_{1}^{2\; j}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{1}^{2j}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{1}^{2j}\left( {2v} \right)} - {W_{N}^{- n}{X_{3}^{2j^{*}}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nv}}}}}} \\{= {\frac{1}{\sqrt{2}}\left\lbrack {{x_{{ref}\; 1}^{e}\left( (n)_{\frac{N}{2}} \right)} - {W_{N}^{- n}{x_{{ref}\; 1}^{o^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right\rbrack}}\end{matrix}\begin{matrix}{{x_{2}^{2\; j}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{2}^{2j}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{2}^{2j}\left( {2v} \right)} - {W_{N}^{- n}{X_{4}^{2j^{*}}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nv}}}}}} \\{= {\frac{1}{\sqrt{2}}\left\lbrack {{x_{{ref}\; 2}^{e}\left( (n)_{\frac{N}{2}} \right)} - {W_{N}^{- n}{x_{{ref}\; 2}^{o^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right\rbrack}}\end{matrix}\begin{matrix}{{x_{3}^{2\; j}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{3}^{2j}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{3}^{2j}\left( {2v} \right)} + {W_{N}^{- n}{X_{1}^{2j^{*}}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nv}}}}}} \\{= {\frac{1}{\sqrt{2}}\left\lbrack {{x_{{ref}\; 1}^{o}\left( (n)_{\frac{N}{2}} \right)} + {W_{N}^{- n}{x_{{ref}\; 1}^{e^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right\rbrack}}\end{matrix}\begin{matrix}{{x_{4}^{2\; j}(n)} = {\frac{1}{\sqrt{N}}{\sum\limits_{k = 0}^{N - 1}\;{{X_{4}^{2j}(k)}W_{N}^{- {nk}}}}}} \\{= {\frac{1}{\sqrt{N}}{\sum\limits_{v = 0}^{\frac{N}{2} - 1}\;{\left( {{X_{4}^{2j}\left( {2v} \right)} + {W_{N}^{- n}{X_{2}^{2j^{*}}\left( {2v} \right)}}} \right)W_{\frac{N}{2}}^{- {nv}}}}}} \\{= {\frac{1}{\sqrt{2}}\left\lbrack {{x_{{ref}\; 2}^{o}\left( (n)_{\frac{N}{2}} \right)} - {W_{N}^{- n}{x_{{ref}\; 2}^{e^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}}} \right\rbrack}}\end{matrix}{{{{where}\mspace{14mu} n} = 0},1,\ldots,{N - 1}}} & (7)\end{matrix}$

Symbols x_(i) ^(2j+1)(n) of the (2j+1)-th block are defined in Equation(8).

$\begin{matrix}{{{x_{1}^{{2j} + 1}(n)} = {\frac{1}{\sqrt{2}}\left\lbrack {{- {x_{{ref}\; 2}^{e^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}} + {W_{N}^{- n}{x_{{ref}\; 2}^{o}\left( (n)_{\frac{N}{2}} \right)}}} \right\rbrack}}{{x_{2}^{{2j} + 1}(n)} = {\frac{1}{\sqrt{2}}\left\lbrack {{- {x_{{ref}\; 1}^{e^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}} - {W_{N}^{- n}{x_{{ref}\; 1}^{o}\left( (n)_{\frac{N}{2}} \right)}}} \right\rbrack}}{{x_{3}^{{2j} + 1}(n)} = {\frac{1}{\sqrt{2}}\left\lbrack {{- {x_{{ref}\; 2}^{o^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}} - {W_{N}^{- n}{x_{{ref}\; 2}^{e}\left( (n)_{\frac{N}{2}} \right)}}} \right\rbrack}}{{x_{4}^{{2j} + 1}(n)} = {\frac{1}{\sqrt{2}}\left\lbrack {{- {x_{{ref}\; 1}^{o^{*}}\left( \left( {- n} \right)_{\frac{N}{2}} \right)}} + {W_{N}^{- n}{x_{{ref}\; 1}^{o}\left( (n)_{\frac{N}{2}} \right)}}} \right\rbrack}}} & (8)\end{matrix}$

The first block 510 corresponding to the j-th block is transmittedthrough the first antenna, the second block 530 corresponding to thej-th block is transmitted through the third antenna, the third block 550corresponding to the j-th block is transmitted through the secondantenna, and the fourth block 570 corresponding to the j-th block istransmitted through the fourth antenna.

Next, the fifth block 520 corresponding to the (j+1)-th block istransmitted through the first antenna, the sixth block 540 correspondingto the (j+1)-th block is transmitted through the third antenna, theseventh block 560 corresponding to the (j+1)-th block is transmittedthrough the second antenna, and the eighth block 580 corresponding tothe (j+1)-th block is transmitted through the fourth antenna.

The STFBC encoder for generating signals is provided with two SFBCencoders. Through these encoders, an SFBC process is performed forblocks between the first and third antennas or the second and fourthantennas. Although two SFBC encoders are provided in the STFBC encoderillustrated in FIG. 4, the above-described operation can be performed inone SFBC encoder.

The SFBC processes are performed on the basis of antenna pairs, i.e., apair of the first and third antennas and a pair of the second and fourthantennas, such that signals whose number corresponds to the number oftransmit antennas are output. During the encoding process of the STBCencoder shown in FIG. 5, the STBC encoder performs the STBC process forgenerating signal blocks mapped to the respective antenna pairs, i.e.,the first signal blocks mapped to the first and third antennas and thesecond signal blocks mapped to the second and fourth antennas.

The first signal blocks are the j-th blocks 510 and 530 and the (j+1)-thblocks 520 and 540 mapped to the first and third antennas. The secondsignal blocks are the j-th blocks 550 and 570 and the (j+1)-th blocks560 and 580 mapped to the second and fourth antennas. The SFBC processis performed for the j-th blocks on the basis of a pair of two antennas(i.e., the pair of the first and third antennas or the second and fourthantennas), such that the signal blocks mapped to the respective antennasare generated.

Next, the STBC process is performed for the generated signal blocks,i.e., between the j-th and (j+1)-th blocks of the first and thirdantennas and the j-th and (j+1)-th blocks of the second and fourthantennas. As a result, the SFBC processes are performed between theantenna pairs and the STBC process is performed for the blocks of theantenna pairs for which the SFBC processes have been performed.

The above-described operations are the STFBC encoding process. The STFBCencoding process generates a sequence in which both the SFBC and STBCprocesses have been applied. The CPs are inserted between the blocks ofthe generated sequence. Thus, the STFBC blocks are transmitted throughthe antennas mapped to the respective blocks using single carriers.

As illustrated in FIG. 5, the four antennas are provided for the STFBCencoding process. When the transmitter structure is extended, astructure of more than four antennas can be exploited.

FIG. 6 illustrates a structure of a receiver in the communication systemusing the STFBC scheme in accordance with the present invention.

The receiver includes a delay unit 601, CP removers 603 and 605, Serialto Parallel Converters (SPCs) 607 and 609, N-FFT processors 611 and 613,a signal detector 615, demultiplexers (DEMUXs) 623 and 625, N/2-FFTprocessors 627, 629, 631, and 633, and a multiplexer (MUX) 635.

Signals of x_(i) ^(2j) and x_(i) ^(2j+1) transmitted from thetransmitter based on the STFBC scheme are shown in Equation (9).x _(i) ^(2j) =[x _(i) ^(2j)(0),x _(i) ^(2j)(1), . . . , x _(i)^(2j)(N−1)]^(T)x _(i) ^(2j+1) =[x _(i) ^(2j+1)(0),x _(i) ^(2j+1)(1), . . . , x _(i)^(2j+1)(N−1)]^(T)  (9)

Herein, i=1, . . . , N_(T) and j=0, . . . , N_(B)/2−1. The receiverreceives the transmitted signals through an antenna. The delay unit 601delays one of the received signals by a regular time. The delayed signalis input into the CP remover 603. The other signal is input into the CPremover 605. The CP removers 603 and 605 remove CPs from the signalreceived from the antenna and the signal output from the delay unit 601.The signals from which the CPs have been removed are output to the SPCs607 and 609.

The signal output from the CP remover 603 is denoted by r^(2j), and thesignal output from the CP remover 605 is denoted by r^(2j+1). r^(2j) andr^(2j+1) can be expressed by Equation (10).

$\begin{matrix}{{r^{2\; j} = {{\sum\limits_{i = 1}^{N_{T}}\;{H_{i}^{2\; j}x_{i}^{2\; j}}} + n^{2\; j}}},{r^{{2\; j} + 1} = {{\sum\limits_{i = 1}^{N_{T}}\;{H_{i}^{{2\; j} + 1}x_{i}^{{2\; j} + 1}}} + n^{{2\; j} + 1}}}} & (10)\end{matrix}$

Herein, H_(i) ^(2j) and H_(i) ^(2j+1) are N×N cyclic channel matrices ofN_(T) transmit antennas, and n^(2j) and n^(2j+1) are Additive WhiteGaussian Noise (AWGN). The SPCs 607 and 609 convert the serial signalsof r^(2j) and r^(2j+1) to parallel signals. The parallel signals areinput to the FFT processors 611 and 613. N-point FFT processes areperformed for the parallel signals. The FFT signals are input into thesignal detector 615. In relation to the received vectors of r^(2j) andr^(2j+1), the signals to be output from the FFT processors 611 and 613are converted to frequency domain signals using an N×N Discrete FourierTransform (DFT) matrix W as shown in Equation (11).

$\begin{matrix}{{R^{2j} = {{\sum\limits_{i = 1}^{N_{T}}\;{{WH}_{i}^{2j}W^{H}X_{i}^{2j}}} + N^{2j}}},} & (11) \\{{R^{{2j} + 1} = {{\sum\limits_{i = 1}^{N_{T}}\;{{WH}_{i}^{{2j} + 1}W^{H}X_{i}^{{2j} + 1}}} + N^{{2j} + 1}}},} & \; \\{{{where}\mspace{14mu} R^{2j}\underset{=}{\Delta}{Wr}^{2j}},{R^{{2j} + 1}\underset{=}{\Delta}{Wr}^{{2j} + 1}},{X_{i}^{2j}\underset{=}{\Delta}{Wx}_{i}^{2j}},} & \; \\{{X_{i}^{{2j} + 1}\underset{=}{\Delta}{Wx}_{i}^{{2j} + 1}},{N_{i}^{2j}\underset{=}{\Delta}{Wn}^{2j}},{{and}\mspace{14mu} N^{{2j} + 1}\underset{=}{\Delta}{{Wn}^{{2j} + 1}.}}} & \;\end{matrix}$

Ψ_(i) ^(2j) and Ψ_(i) ^(2j+1), corresponding to N×N diagonal matriceswith Fourier transform values of channel impulse responses are definedas shown in Equation (12).Ψ_(i) ^(2j) ΔWH_(i) ^(2j)W^(H), Ψ_(i) ^(2j+1) ΔWH_(i) ^(2j+1)W^(H)  (12)

The signal detector 615 for receiving the output signal R^(2j) of theFFT processor 611 and the output signal R^(2j+1) of the FFT processor613 includes a linear combiner 617, a simultaneous equation solver 619,and a SC Minimum Mean Square Error-Frequency Domain Equalization (SCMMSE-FDE) processor 621.

The linear combiner 617 receives the frequency domain signals R^(2j) andR^(2j+1). R^(2j) and R^(2j+1) are expressed by Equation (13).R ₁=Λ₁ X ₁+Λ₂ X ₂+Λ₃ X ₃+Λ₄ X ₄ +N ₁R ₂=−Λ₁ X ^(·) ₂+Λ₂ X ^(·) ₁−Λ₃ X ^(·) ₄+Λ₄ X ^(·) ₃ +N ₂R ₃=−Λ₁ X ^(·) ₃−Λ₂ X ^(·) ₄+Λ₃ X ^(·) ₁+Λ₄ X ^(·) ₂ +N ₃R ₄=Λ₁ X ₄−Λ₂ X ₃−Λ₃ X ₂+Λ₄ X ₁ +N ₄  (13)

Herein, Λ_(i) is diagonal elements of Ψ_(i) ^(2j) and Ψ_(i) ^(2j+1),where i has a value between 1 and N_(T). Thus, the linear combiner 617combines the output signals of the FFT processors 611 and 613. Forexample, the signal combination is shown in Equation (14).

$\begin{matrix}\begin{matrix}{\overset{\sim}{X} = {\begin{bmatrix}{\overset{\; \sim}{X_{1}}\;} \\{\overset{\; \sim}{X_{2}}\;} \\{\overset{\; \sim}{X_{3}}\;} \\{\overset{\; \sim}{X_{4}}\;}\end{bmatrix} = {{\begin{bmatrix}\Theta & 0 & 0 & \Phi \\0 & \Theta & {- \Phi} & 0 \\0 & {- \Phi} & \Theta & 0 \\\Phi & 0 & 0 & \Theta\end{bmatrix}\begin{bmatrix}X_{1} \\X_{2} \\X_{3} \\X_{4}\end{bmatrix}} + \begin{bmatrix}{\overset{\; \sim}{N_{1}}\;} \\{\overset{\; \sim}{N_{2}}\;} \\{\overset{\; \sim}{N_{3}}\;} \\{\overset{\; \sim}{N_{4}}\;}\end{bmatrix}}}} \\{= {{\overset{\sim}{\Lambda}X^{\prime}} + \overset{\sim}{N}}} \\{\Theta = \left( {{\Lambda_{1}}^{2} + {\Lambda_{2}}^{2} + {\Lambda_{3}}^{2} + {\Lambda_{4}}^{2}} \right)} \\{\Phi = \left( {{\Lambda_{1}\Lambda_{4}^{*}} + {\Lambda_{1}^{*}\Lambda_{4}} - {\Lambda_{2}\Lambda_{3}^{*}} - {\Lambda_{2}^{*}\Lambda_{3}}} \right)} \\{\overset{\sim}{N_{1}} = {{\Lambda_{1}^{*}N_{1}} + {\Lambda_{2}N_{2}^{*}} + {\Lambda_{3}N_{3}^{*}} + {\Lambda_{4}^{*}N_{4}}}} \\{{\overset{\sim}{N}}_{2} = {{\Lambda_{2}^{*}N_{1}} - {\Lambda_{1}N_{2}^{*}} + {\Lambda_{4}N_{3}^{*}} - {\Lambda_{3}^{*}N_{4}}}} \\{{\overset{\sim}{N}}_{3} = {{\Lambda_{3}^{*}N_{1}} + {\Lambda_{4}N_{2}^{*}} - {\Lambda_{1}N_{3}^{*}} - {\Lambda_{2}^{*}N_{4}}}} \\{{\overset{\sim}{N}}_{4} = {{\Lambda_{4}^{*}N_{1}} - {\Lambda_{3}N_{2}^{*}} - {\Lambda_{2}N_{3}^{*}} + {\Lambda_{1}^{*}N_{4}}}}\end{matrix} & (14)\end{matrix}$

Equation (14) is a result obtained by changing a matrix form throughMaximal Ratio Combining (MRC). The MRC method combines signals accordingto ratio based on the best performance.

The simultaneous equation solver 619 solves simultaneous equations usingthe output signal of the linear combiner 617. Elements of Equation (14)are multiplied by Φ because of a 4×4 matrix that does not have the fullrank.

Thus, components other than original signals are to be removed. Forthis, the simultaneous equations are solved. The simultaneous equationsolver 619 computes output noise power of a linearly combined signal.The output noise power is shown in Equation (15).

$\begin{matrix}\begin{matrix}\begin{matrix}{\sigma_{n,{eq}}^{2}\overset{\Delta}{=}{{E\left\{ {\left( {{\Theta\Lambda}_{1}^{*} - {\Phi\Lambda}_{4}^{*}} \right){N_{1} \cdot \left( {{\Theta\Lambda}_{1} - {\Phi\Lambda}_{4}} \right)}N_{1}^{*}} \right\}} +}} \\{{E\left\{ {\left( {{\Theta\Lambda}_{2} + {\Phi\Lambda}_{3}} \right){N_{2}^{*} \cdot \left( {{\Theta\Lambda}_{2}^{*} + {\Phi\Lambda}_{3}^{*}} \right)}N_{2}} \right\}} +} \\{{E\left\{ {\left( {{\Theta\Lambda}_{3} + {\Phi\Lambda}_{2}} \right){N_{3}^{*} \cdot \left( {{\Theta\Lambda}_{3}^{*} + {\Phi\Lambda}_{2}^{*}} \right)}N_{3}} \right\}} +} \\{E\left\{ {\left( {{\Theta\Lambda}_{4}^{*} - {\Phi\Lambda}_{1}^{*}} \right){N_{4} \cdot \left( {{\Theta\Lambda}_{4} - {\Phi\Lambda}_{1}} \right)}N_{4}^{*}} \right\}}\end{matrix} \\{= {{\left( {{\Theta^{2}{\Lambda_{1}}^{2}} + {\Phi^{2}{\Lambda_{4}}^{2}} - {{\Theta\Phi\Lambda}_{1}^{*}\Lambda_{4}} - {{\Theta\Phi\Lambda}_{1}\Lambda_{4}^{*}}} \right)N_{0}} +}} \\{{\left( {{\Theta^{2}{\Lambda_{2}}^{2}} + {\Phi^{2}{\Lambda_{3}}^{2}} + {{\Theta\Phi\Lambda}_{2}^{*}\Lambda_{3}} + {{\Theta\Phi\Lambda}_{2}\Lambda_{3}^{*}}} \right)N_{0}} +} \\{{\left( {{\Theta^{2}{\Lambda_{3}}^{2}} + {\Phi^{2}{\Lambda_{2}}^{2}} + {{\Theta\Phi\Lambda}_{2}^{*}\Lambda_{3}} - {{\Theta\Phi\Lambda}_{2}\Lambda_{2}^{*}}} \right)N_{0}} +} \\{\left( {{\Theta^{2}{\Lambda_{4}}^{2}} + {\Phi^{2}{\Lambda_{1}}^{2}} - {{\Theta\Phi\Lambda}_{1}^{*}\Lambda_{4}} - {{\Theta\Phi\Lambda}_{1}\Lambda_{4}^{*}}} \right)N_{0}} \\{= {\left\lbrack {{\left( {\Theta^{2} + \Phi^{2}} \right)\Theta} + {{\Theta\Phi}\left( {- \Phi} \right)} + {{\Theta\Phi}\left( {- \Phi} \right)}} \right\rbrack N_{0}}} \\{= {\left( {\Theta^{2} - \Phi^{2}} \right) \cdot \Theta \cdot N_{0}}}\end{matrix} & (15)\end{matrix}$

Upon receiving a signal obtained by solving the simultaneous equations,the SC MMSE-FDE processor 621 performs a frequency domain equalizationprocess. The SC MMSE-FDE processor 621 applies an MMSE technique to theoutput signal of the simultaneous equation solver 619. At this time, aresulting signal is shown in Equation (16).

$\begin{matrix}{\begin{matrix}{Y = \begin{bmatrix}{{\Theta\;{\overset{\sim}{X}}_{1}} - {\Phi\;{\overset{\sim}{X}}_{4}}} \\{{\Theta\;{\overset{\sim}{X}}_{2}} + {\Phi\;{\overset{\sim}{X}}_{3}}} \\{{\Theta\;{\overset{\sim}{X}}_{3}} + {\Phi\;{\overset{\sim}{X}}_{2}}} \\{{\Theta\;{\overset{\sim}{X}}_{4}} - {\Phi\;{\overset{\sim}{X}}_{1}}}\end{bmatrix}} \\{= {{\begin{bmatrix}{\Theta^{2} - \Phi^{2}} & 0 & 0 & 0 \\0 & {\Theta^{2} - \Phi^{2}} & 0 & 0 \\0 & 0 & {\Theta^{2} - \Phi^{2}} & 0 \\0 & 0 & 0 & {\Theta^{2} - \Phi^{2}}\end{bmatrix}X^{\prime}} + \overset{ˇ}{N}}} \\{{= {{\Gamma\; X^{\prime}} + \overset{ˇ}{N}}},}\end{matrix}{{Q\overset{\Delta}{=}{\frac{\Gamma^{*}}{\Gamma^{2} + {\frac{\sigma_{n,{eq}}^{2}}{\sigma_{x}^{2}}I_{\hat{}}}} = \frac{1}{\Gamma + {\frac{\Theta\; N_{0}}{\sigma_{s}^{2}}I_{4}}}}},{{\therefore\hat{X}} = {{QY} = {\left( {\Gamma + {\frac{\Theta\; N_{0}}{\sigma_{s}^{2}}I_{4}}} \right)^{- 1}Y}}}}} & (16)\end{matrix}$

The simultaneous equation solver 619 computes a mean value of outputsignals of the linear combiner 617. The mean value is computed usingEquation (17).BA ₁ +CA ₄ =X ₁(B ² −C ²)+N ₁(BΛ ^(·) ₁ −CΛ ^(·) ₄)+N ^(·) ₂(BΛ ₂ +CΛ₃)+N ^(·) ₃(BΛ ₃ +CΛ ₂)+N ₄(BΛ ^(·) ₄ −CΛ ^(·) ₁)BA ₂ +CA ₃ =X ₂(B ² −C ²)+N ₁(BΛ ^(·) ₂ +CΛ ^(·) ₃)+N ^(·) ₂(−BΛ ₁ +CΛ₄)+N ^(·) ₃(BΛ ₄ −CΛ ₁)−N ₄(BΛ ^(·) ₄ +CΛ ^(·) ₂)BA ₃ +CA ₂ =X ₃(B ² −C ²)+N ₁(CΛ ^(·) ₂ +BΛ ₃ ^(·))+N ^(·) ₂(−CΛ ₁ +BΛ₄)+N ^(·) ₃(CΛ ₄ −BΛ ₁)−N ₄(BΛ ^(·) ₄ +CΛ ^(·) ₂)BA ₄ +CA ₁ =X ₄(B ² −C ²)+N ₁(CΛ ^(·) ₁ −BΛ ^(·) ₄)+N ^(·) ₂(CΛ ₂ +BΛ₃)+N ^(·) ₃(CΛ ₃ +BΛ ₂)+N ₄(BΛ ^(·) ₄ −BΛ ^(·) ₁)  (17)

The SC MMSE-FDE processor 621 performs a frequency domain equalizationprocess using the mean value of the simultaneous equation solver 619.The SC MMSE-FDE processor 621 computes an MMSE and performs a signalcombination and signal detection. Because a signal is detected using theMMSE, a total estimation error is minimized. Thus, the signal detectionis effectively performed for a fading channel with a null.

A signal output through the combination of the SC MMSE-FDE processor 621is shown in Equation (18).

$\begin{matrix}{\begin{matrix}{Y = \begin{bmatrix}{{\Theta\;{\overset{\sim}{X}}_{1}} - {\Phi\;{\overset{\sim}{X}}_{4}}} \\{{\Theta\;{\overset{\sim}{X}}_{2}} + {\Phi\;{\overset{\sim}{X}}_{3}}} \\{{\Theta\;{\overset{\sim}{X}}_{3}} + {\Phi\;{\overset{\sim}{X}}_{2}}} \\{{\Theta\;{\overset{\sim}{X}}_{4}} - {\Phi\;{\overset{\sim}{X}}_{1}}}\end{bmatrix}} \\{= {{\begin{bmatrix}{\Theta^{2} - \Phi^{2}} & 0 & 0 & 0 \\0 & {\Theta^{2} - \Phi^{2}} & 0 & 0 \\0 & 0 & {\Theta^{2} - \Phi^{2}} & 0 \\0 & 0 & 0 & {\Theta^{2} - \Phi^{2}}\end{bmatrix}X^{\prime}} + \overset{ˇ}{N}}} \\{{= {{\Gamma\; X^{\prime}} + \overset{ˇ}{N}}},}\end{matrix}{{Q\overset{\Delta}{=}{\frac{\Gamma^{*}}{\Gamma^{2} + {\frac{\sigma_{n,{eq}}^{2}}{\sigma_{x}^{2}}I_{\hat{}}}} = \frac{1}{\Gamma + {\frac{\Theta\; N_{0}}{\sigma_{s}^{2}}I_{4}}}}},{{\therefore\hat{X}} = {{QY} = {\left( {\Gamma + {\frac{\Theta\; N_{0}}{\sigma_{s}^{2}}I_{4}}} \right)^{- 1}Y}}}}\begin{matrix}{{\hat{X} = \left\lbrack {{\hat{X}}_{1}{\hat{X}}_{2}{\hat{X}}_{3}{\hat{X}}_{4}} \right\rbrack^{T}};} \\{{{\hat{X}}_{1} = {\hat{X}}_{{ref}\; 1}^{e}},} \\{{{\hat{X}}_{2} = {\hat{X}}_{{ref}\; 2}^{e}},} \\{{{\hat{X}}_{3} = {\hat{X}}_{{ref}\; 1}^{o}},} \\{{\hat{X}}_{4} = {\hat{X}}_{{ref}\; 2}^{o}}\end{matrix}} & (18)\end{matrix}$

{hacek over (N)} corresponding to noise can be expressed by [{circumflexover (N)}₁{circumflex over (N)}₂{circumflex over (N)}₃{circumflex over(N)}₄]^(T). σ_(x) ² denotes the desired signal power. Using Equation(17), the signal detector detects signals and inputs the detectedsignals to the DEMUXs 623 and 625. The DEMUXs 623 and 625 demultiplexthe detected signals. The detected signals are {circumflex over(X)}_(ref 1) and {circumflex over (X)}_(ref 2). The DEMUX 623 receives{circumflex over (X)}_(ref 1) and the DEMUX 625 receives {circumflexover (X)}_(ref 2). The demultiplexed detected signals are output to theFFT processors 627, 629, 631, and 632. At this time, the DEMUX 623outputs signals of {circumflex over (X)}_(ref 1) ^(e) and {circumflexover (X)}_(ref 2) ^(e) and the DEMUX 625 outputs signals of {circumflexover (X)}_(ref 1) ^(o) and {circumflex over (X)}_(ref 2) ^(o). Theoutput signals are input to the FFT processors 627, 629, 631, and 633.The FFT processors 627, 629, 631, and 633 perform N/2-point FFTprocesses. At this time, the FFT processors 627, 629, 631, and 633receive the {circumflex over (X)}_(ref 1) ^(e), {circumflex over(X)}_(ref 2) ^(e), {circumflex over (X)}_(ref 1) ^(o), and {circumflexover (X)}_(ref 2) ^(o) signals, respectively, and perform the FFTprocesses for the received signals. The FFT signals are output to theMUX 635. The MUX 635 multiplexes the received FFT signals.

Next, the proposed STFBC scheme will be described with reference to FIG.7, where the graph was obtained by measuring Bit Error Rates (BERs) inthree 4×1 antenna systems based on the STBC, SFBC, and STFBC schemes. Inrelation to the graph shown in FIG. 7, a block with a size of 256symbols and a Quadrature Phase Shift Keying (QPSK) modulation schemewere used. Furthermore, a single carrier, a center frequency band of 2GHz, and a bandwidth of 5 MHz were used.

From FIG. 7, it can be seen that the system based on the STFBC schemeoutperforms the STBC system and the SFBC system.

As described above, the present invention employs the STFBC scheme inwhich both STBC and SFBC schemes are applied, thereby avoiding systemperformance degradation in a fast fading channel and a frequencyselective fading channel of a communication system using the existingSTBC and SFBC schemes.

Although preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions, and substitutions arepossible, without departing from the scope of the present invention.Therefore, the present invention is not limited to the above-describedembodiments, but is defined by the following claims, along with theirfull scope of equivalents.

1. A method for transmitting a signal in a wireless communication systemcomprising a transmitter with at least four transmit antennas and areceiver with at least one receive antenna, the method comprising: a)performing Space Frequency Block Coding (SFBC) processes for blocks tobe transmitted through each of two antenna pairs and outputting signalblocks on which SFBC has been performed whose number corresponds to thenumber of transmit antennas; and b) performing a Space Time Block Coding(STBC) process for the signal blocks generated according to the antennapairs, consecutively, and transmitting signals carried by singlecarriers through the at least four transmit antennas mapped to thesignal blocks, wherein step a) comprises: performing an SFBC process forsignals to be transmitted through first and third antennas andoutputting first signal blocks mapped to the first and third antennas;and performing an SFBC process for signals to be transmitted throughsecond and fourth antennas and outputting second signal blocks mapped tothe second and fourth antennas.
 2. The method of claim 1, wherein thesignals obtained by performing the STBC process for the first and secondsignal blocks are transmitted through the at least four transmitantennas.
 3. The method of claim 1, wherein guard intervals are insertedbetween the blocks for which the STBC process has been performed.
 4. Anapparatus for transmitting a signal in a wireless communication systemcomprising a transmitter with at least four transmit antennas and areceiver with at least one receive antenna, the apparatus comprising: asymbol mapper for mapping an input bit stream to a symbol of apredetermined length; a Space Time Frequency Block Code (STFBC) encoderfor performing Space Frequency Block Coding (SFBC) processes for blocksto be transmitted through each of two antenna pairs, outputting signalblocks on which SFBC has been performed whose number corresponds to thenumber of transmit antennas, and performing a Space Time Block Coding(STBC) process for the signal blocks generated according to the antennapairs, consecutively; and guard interval inserters for inserting guardintervals into output signals of the STFBC encoder and transmitting thesignals into which the guard intervals have been inserted through the atleast four transmit antennas, wherein the STFBC encoder comprises: afirst SFBC encoder for performing an SFBC process for signals to betransmitted through first and third antennas and outputting first signalblocks mapped to the first and third antennas; and a second SFBC encoderfor performing an SFBC process for signals to be transmitted throughsecond and fourth antennas and outputting second signal blocks mapped tothe second and fourth antennas.
 5. The apparatus of claim 4, furthercomprising: an STBC encoder for performing the STBC process for thefirst and second signal blocks.